This invention relates to power steering systems for automotive vehicles and, more particularly, to a damper for a rack and pinion power steering system in an automotive vehicle.
Steering systems on vehicles equipped with a rack and pinion-type steering frequently experience high speed steering wheel shake. High-speed shake of the steering wheel is detrimental to the feel of the steering. Prior attempts to reduce or eliminate such high-speed shake or vibrations have proven unsuccessful. The normal means of attenuating high-speed shake are ineffective on vehicles with rack and pinion-type steering systems. The primary reason that prior attempts to reduce or eliminate high-speed shake and vibrations of this type have not been effective for rack and pinion-type systems are the mounting and frequency requirements.
Previously, linear dampers were used to dampen steering wheel oscillations or vibrations. Linear dampers are commonly effective on larger vehicles, which have large displacement steering systems because the linear damper devices focus on the steering system velocity. Rack and pinion-type systems typically have a high frequency and low amplitude vibration or shake and linear dampers are not adequately suited to address vibrations of this type. The low amplitude vibration does not provide sufficient velocity for the linear damper to effectively operate.
Other devices which have been used to address high-speed steering wheel shake include constant friction-type interfaces. However, such approaches have also proven to be unacceptable for rack and pinion-type steering systems because the feel and return to center characteristics of the steering system are detrimentally impacted or destroyed with constant friction-type interfaces.
Therefore, a need exists for a damper for high speed shake and vibrations of high frequency and low amplitude in rack and pinion-type systems while still providing good responsive feeling to the steering wheel and return to center characteristics.
This invention solves the above-described and other problems common in vehicle rack and pinion-type steering systems. The present invention offers a good responsive feel in a neutral position of the steering wheel during high speed running of the vehicle and desirable return to center characteristics of the steering system.
In one embodiment of this invention, a power steering system for a vehicle includes a steering wheel coupled to a rack and pinion assembly. A damper is coupled to the pinion of the rack and pinion assembly and is also in hydraulic communication with a pressure pump. The damper includes a generally fixed housing having a keyway on an interior surface of the housing. A steering shaft is inserted into the housing and includes a spline portion and an output end, which is coupled to the pinion of the rack and pinion assembly. A clutch in the housing engages the spline portion of the steering shaft as well as the keyway on the interior of the housing. The clutch is biased by a spring to inhibit rotation of the steering shaft relative to the housing and thereby dampen the high-speed shake, vibrations or other oscillations being transmitted in the power steering system. The damper locks or inhibits the steering shaft from rotating relative to the housing while the vehicle is traveling straight down the road to absorb the input energy and cancel any vibration from the wheels, suspension or road.
The clutch is automatically disengaged upon movement of the steering wheel by an operator. Pressure from the power steering pump increases when there is steering wheel input and the increase in pressure is communicated through a port in the housing of the damper to release the clutch and allow the steering to turn freely. When the pressure in the power steering pump increases, the pressure in the damper likewise increases to thereby disengage the clutch by overcoming the bias of the springs and allowing the steering shaft to turn freely.
In one embodiment, the clutch utilizes a multi-disk arrangement with two types of disks. Disks of the first type are each interposed between a pair of disks of the second type. The first type of disk includes a tooth on an inner circumference thereof, which engages the spline portion of the steering shaft. The second type of disk includes a key on an outer circumference thereof, which engages the keyway on the interior of the fixed housing. The spring in the damper biases the disks into engagement with each other thereby inhibiting or preventing rotation of the first type of disk relative to the second type of disk and likewise rotation of the steering shaft relative to the housing to dampen vibrations or high speed shake being transmitted in the power steering system. Once the operator moves the steering wheel, the pressure in the hydraulic pump increases which is communicated to the interior of the damper housing through the port. The increase in pressure acts on a piston positioned between the disks and the spring to thereby compress the spring and release the disks for rotation relative to each other. Once the disks are permitted to rotate relative to each other, the steering shaft rotates relative to the housing to provide normal steering operation of the vehicle.